This application is based on Application No. 2001-183000, filed in Japan on Jun. 18, 2001, the contents of which are hereby incorporated by reference.
1. Field of the Invention
The present invention relates to a control system for an internal combustion engine, and in particular to a technique for controlling ignition timing, fuel injection timing and an amount of fuel injection.
2. Description of the Related Art
Major control functions of a control system for an internal combustion engine include ignition timing control for ignition coils, and fuel injection timing control and fuel injection amount control for fuel injectors. Here, note that for timing control of ignition timing and fuel injection timing, there is generally employed a method (cycle prediction method) in which a current cycle or period between reference signals representative of reference positions of the rotation of an engine (i.e., cycle or period between predetermined fixed angles) is measured and the next prescribed cycle or period is estimated or predicted based on the current cycle or period thus measured.
FIG. 13 is an explanatory view illustrating the cycle prediction method. First of all, a reference signal is generated by a reference signal generator at each timing, for instance, at time points tn-2, tn-1 and tn, respectively, as shown in FIG. 13. Here, assuming tn as the current timing (time), a current measured cycle T(n) can be calculated as follows: T(n)=tnxe2x88x92tn-1. Then, the next estimated or predicted cycle T(F) is calculated as follows: T(F)=T(n)xc2x1xcex1, where xcex1 is a correction factor to be described later. Based on these measured and estimated cycles, a variety of kinds of timing control operations are carried out.
FIG. 14 illustrates the configuration of such a kind of known control system for an internal combustion engine. In FIG. 14, the known control system includes an internal combustion engine control unit (ECU) 1, a reference signal generator 3, an ignition (IG) coil 8 and a fuel injector 10. The ECU 1 includes a CPU 2 acting as an arithmetic processing section, a reference signal input I/F circuit 5, an IG coil drive I/F circuit 7 connected with the ignition (IG) coil 8, and an injector drive I/F circuit 9 connected with the fuel injector 10.
FIG. 15 illustrates a time chart of signals at respective portions of the system of FIG. 14.
Now, reference will be made to the operation of the known control system for an internal combustion engine while referring to FIGS. 14 and 15. A signal is generated by the reference signal generator 3 at predetermined timing, so that reference timing is input to the CPU 2 in the ECU 1 via the reference signal input I/F circuit 5. When this reference timing is input to the CPU 2, a reference signal interrupt is generated in the processing of the CPU 2, whereby the CPU 2 performs processing of the ignition timing, the fuel injection timing and the fuel injection amount for a cylinder which has generated the current interrupt.
For instance, the CPU 2 sets an energization start timing T1 and an ignition (cut-of timing T2 (see a signal S2 for these timing) for the IG coil 8 to a prescribed timer. Also, the CPU sets a fuel injection start timing T0 (see a signal S4) to another prescribed timer. When each timer with these timing set therein counts a predetermined period of time (time duration), an interrupt is generated to perform output processing so that output signals are sent from these timers to the corresponding drive I/F circuits 7, 9, respectively.
As shown in FIG. 15 for example, with an interrupt of the IG coil energization start timing T1, the output S2 of the CPU 2 to the IG coil drive I/F circuit 7 is switched from a low (L) level to a high (H) level, whereas at the IG coil ignition (cut-off) timing T2, the output S2 is switched from the H level to the L level, thereby causing the IG coil 8 to generate an ignition output.
At the fuel injection start timing T0, an output S4 of the CPU 2 to the injector drive I/F circuit 9 is switched from the L level to the H level, and at the same time a pulse width (time duration) TP corresponding to an amount of injection is set to a prescribed timer whereby a predetermined amount of fuel can be supplied from the injector 10.
In the case of this cycle prediction method, the accuracy of the next prediction cycle becomes an important parameter for control. That is, if the prediction cycle or period is inaccurate, there will be errors or deviations in the ignition timing and the fuel injection timing, thus giving rise to a possibility of adversely affecting the driving and operation of an associated internal combustion engine.
At present, in order to improve the accuracy of the above-mentioned cycle prediction, various corrections are carried out for engine operating conditions (e.g., the prediction cycle is set to be shorter during acceleration, and longer during deceleration), or the intervals between pulses of the reference signal are shortened to absorb and make it possible to detect variations in rotation of the engine for improved accuracy.
In the above circumstances, the above-mentioned ignition timing and the fuel injection timing are important items for engine output power and its stability in internal combustion engines, and hence high accuracy is demanded for these important items. Particularly, in the system of a direct-injection method in which fuel is injected directly into engine cylinders, accuracy in fuel injection timing is required to be higher than before, and hence is becoming an even more important item. In addition, in the case of two-cycle engines, variations in the number of revolutions per minute of the engine are great due to engine structures, and hence, there arises a problem that an accurate cycle prediction is difficult.
The present invention is intended to obviate the problem as referred to above, and has for its object to provide a control system for an internal combustion engine which is capable of controlling ignition timing and fuel injection timing in a stable manner at any time even in an engine, or in an operating range or in an operating condition, in which there are great variations in the number of revolutions per minute of the engine.
Bearing the above object in mind, the present invention resides in a control system for an internal combustion engine, including: a reference signal generator for generating a reference signal representative of a reference position of the rotation of the engine; a fixed angle signal generator for generating a fixed angle signal which has a resolution higher than that of the reference signal and which is representative of a rotational position of the engine; and an internal combustion engine control unit with an arithmetic processing section operable to receive the reference signal and the fixed angle signal and control ignition timing and fuel injection timing based on a count value of the fixed angle signal with the reference signal taken as a reference, the internal combustion engine control unit being also operable to control a fuel injection amount by a time measurement.
In a preferred form of the present invention, the internal combustion engine control unit includes a storage section for storing a table including crank angles representative of engine rotational positions of the ignition timing and the fuel injection timing and a fuel injection time representative of the fuel injection amount for determining ideal ignition timing, ideal fuel injection timing and an ideal fuel injection amount in each engine operating condition. The arithmetic processing section comprises counters for counting the fixed angle signal up to set values of the crank angles, respectively, which are set in accordance with the table so as to control the ignition timing and the fuel injection timing, and a timer for measuring time up to a set value of a time which is set in accordance with the table so as to control the fuel injection amount.
In another preferred form of the present invention, the fixed angle signal generator includes a ring gear operable to rotate in synchronization with the rotation of the engine, and a rotation sensor for detecting a tooth of the ring gear and generating the corresponding fixed angle signal. The internal combustion engine control unit includes a fixed angle signal I/F circuit for generating four pulses from one tooth of the ring gear based on the fixed angle signal from the rotation sensor.
In a further preferred form of the present invention, the fixed angle signal I/F circuit includes a full-wave rectifier circuit for full-wave rectifying the fixed angle signal from the rotation sensor to generate a full-wave rectified signal, a regular interval pulse shaping circuit for slicing the full-wave rectified signal at a predetermined voltage level to generate a pulse signal of a xc2xd duty ratio, and a pulse circuit for generating a pulse every time the pulse signal output from the regular interval pulse shaping circuit rises or falls.
In the present invention, a control system for an internal combustion engine includes a reference signal generator for generating a reference signal of the engine, a fixed angle signal generator for generating a fixed angle (high resolution) signal of the engine, and an internal combustion engine control unit (ECU) with a CPU acting as an arithmetic processing section for generating drive signals to an ignition (IG) coil and a fuel injector based on the reference signal and the fixed angle signal thereby to control ignition timing, fuel injection timing and a fuel injection amount.
By angle counting using the reference signal and the fixed angle signal, the CPU controls the ignition timing, which includes an energization start time point and an ignition time point for the IG coil, and the fuel injection timing (drive timing), which is a fuel injection start time point of the fuel injector. Also, the CPU controls the fuel injection amount (drive time) by using a timer (time) in the CPU. As a result, it becomes possible to stably control the ignition timing, the fuel injection timing and the fuel injection amount at any time even in an engine, or in an operating range, or in an operating condition, in which variations in the number of revolutions per minute of the engine are great.
In addition, the ECU further includes an input I/F circuit for the fixed angle signal which serves to improve the resolution of the fixed angle signal to be input thereto.
The above and other objects, features and advantages of the present invention will become more readily apparent to those skilled in the art from the following detailed description of preferred embodiments of the present invention taken in conjunction with the accompanying drawings.